(1) Field of the Invention
This invention pertains to emulsifiers which give improved adhesion when used to prepare adhesive polymeric latices by emulsion polymerization. More particularly, it relates to emulsifiers which are more effective than conventional emulsifiers allowing reduced levels to be used to produce equivalent stability in a dispersed adhesive latex system.
(2) Description of the Prior Art
Emulsion polymers are often used in synthetic adhesives and coatings production. Preparation involves the initiation of polymerization of one or more ethylenically unsaturated monomers in the presence of an aqueous phase containing a suitable emulsifying agent or combination of agents. Emulsifying agents are generally anionic, but sometimes are nonionic or cationic in electrolytic charge of the organic fraction. Among the anionic emulsifying agents utilized for this application are water-soluble soaps, such as alkali metal oleates, stearates, or rosin acids, sulfates of higher alcohols, such as sodium lauryl sulfate, sulfonates of alkyl acyl hydrocarbons such as dodecylbenzene sulfonate, sulfonated alfa-olefins, polyether alcohols and a host of analogous and similar surface active emulsifying agents. U.S. Pat. No. 3,505,265 teaches certain divalent salts of alkylated diphenyl ether sulfonates as emulsion polymerization emulsifiers.
The total amount of the emulsifying agent in adhesive latices generally ranges from about 2 to 5 parts per 100 parts of monomer used in the polymerization. This amount is required so that the latex will remain stable to coagulation during handling and further processing. Much of the total emulsifier adsorbs to the individual latex particle surfaces and the higher the emulsifier level, the greater the extent to which the particle surfaces are covered. The emulsion polymer is generally formulated with pigments or extenders and other additives to a variety of coating compositions. Such ingredients compete with the emulsion polymer surface for emulsifier. Since uncoated particle surface is also needed for interaction with compounding ingredients such as thickeners, low emulsifier coverage contributes to minimum quantities of such ingredients being required. Further, excessive colloidal stability of the compounding system requires greater water removal before the emulsion polymer coagulates to adhere the coating components together and to the substrate. Thus, the minimum of emulsifying agent that provides adequate colloidal stability for handling and processing helps insure quick coagulation and fewer problems in drying the coating.
Therefore, it is the object of the present invention to provide emulsion polymerization emulsifiers which produce adhesive and coating compositions with improved adherence to the substrate material. It is a further object to provide emulsion polymerization emulsifiers which when employed in aqueous adhesive and coating compositions in reduced amounts produce adequate stability and yet provide rapid coagulation and improved drying.